There is always a wasabi in my fridge.

Wasabi is an uncountable noun, it's a paste, so you can have 'some wasabi' or 'a packet of wasabi'... you could also have 'a bottle of wasabi' , I hope this makes sense to you!

and, I like to buty a wasabi taste snack at the supermarket.

You can use 'a' here because you're talking about buying 'a snack' and using 'wasabi' to describe what type of snack it is. I took out 'taste' because it doesn't really make sense unless the snack was named 'Wasabi Taste'. You might have wanted to say: ' I like to buy a tasty wasabi snack at the supermarket'.

I think when people gotbecome adults their favourite flavour changes.

You can either say: 'their favourite flavours change' or 'their favourite flavour changes'.

I added a 'u' to the spelling of flavour because you chose the British spelling of favourite. Without the 'u' is the US spelling. Obviously, the British version is the best ;)

I didn'tnever use to eat wasabi when I was child.

Now It iit’s essential in my life when I eat tofu or rice.

There i’s always a wasabi in my fridge.

and, I like to buty a wasabi tasteflavoured snack at the supermarket.

They a’re delicious.

I think when people got adultsrow up their favourite flavour changes.

‘become adults’ is also acceptable.

For ‘favourite’ you have used the British English spelling, but for ‘flavor’ the American English spelling. Both are correct, but be consistent.